Several types of useful precision tools and instruments consist of a plurality of elongated members pivotally fastened together at a point close to one end of the elongated members. Typical examples include dental pliers, scissors, cutters, and a broad variety of other precision tools used in several fields, including medicine, dentistry and instrumentation.
Typically, the pivotal members of the tool are pivotally affixed to one another with a threaded screw. Unfortunately, such fastening means often loosens during use, reducing the effectiveness of the tool. Further, when an expensive precision tool has a worn fastener, such that it cannot be tightened to provide precision mating of the jaws, the tool must often be replaced at considerable expense, with some dental tools costing between 50 and 100 dollars.
One way of avoiding this problem is to use a rivet in place of the screw. This solution is not entirely satisfactory, however, because it is difficult to control the precise binding pressure on the pivotal joint. In addition, the stresses placed upon the rivet during use often cause it to deform, similarly causing loosening of the pivotal members and an associated loss in tool effectiveness. Unlike the threaded screw, moreover, it is difficult to again increase the attachment force once deformation of the rivet has occurred. A rivet also makes it difficult to detach the tool members for cleaning, sharpening or replacement.
Another problem with existing fasteners for pivotal tools appears in the assembly process. Specifically, it is often desirable that the pressure asserted by the fastening means be relatively the same for each tool. In practice, this requires testing and readjustment during the assembly process. Not only does this increase the complexity of tool assembly, but also the difficulties a user may encounter when he must retighten the fastening means after some use.
In short, there has been a continuing need for a fastener for pivotal tool members which will not come loose during normal use, which consistently achieves the desired attachment force, and which may be readily reset to the proper tightness in case of looseness resulting from any occurrence.